The number of women in jail is reportedly skyrocketing, but no one knows why

An inmate is checked into the Orange County jail in Santa Ana, California, on May 24, 2011. Reuters/Lucy Nicholson Amid a fierce national debate on mass incarceration in the US, a new report has found that one population has been severely overlooked: women.

The number of women held in local US jails has skyrocketed over the last four decades, jumping as much as 14 times what it was in the 1970s, according to a report jointly released on Wednesday by the Vera Institute of Justice, an independent research nonprofit that "tackles the most pressing injustices of our day," and the MacArthur Foundation's Safety and Justice Challenge, which is aimed at improving local justice systems.

Women now make up nearly 110,000 of the 745,000 people in the country's jails, the report found.

Beyond the "alarming" rate increase, the report concludes that the criminal-justice system is sorely lacking in research and data on why more women are being locked up.

"With little data and scant examination of just who the women in jail are and how they got there, it is not surprising that recent innovations to craft smarter, more targeted use of jails do not account for the realities of women's lives," Fred Patrick, a director at the Vera Institute of Justice, said in the report.

What little is known about these female inmates is that the majority are charged with low-level, nonviolent offenses and typically have less extensive criminal histories than male inmates.

Further, nearly 80% of women in jail are mothers, many of whom bear sole responsibility for their children, according to the report.

The report found that several factors affect women's incarceration to a greater extent than men, including trauma, physical and behavioral health disorders, single-parenting, and poverty.

Local jurisdictions have let jails become "stopgap providers" of social and community services for women, who were unable to reach resources they needed outside of the criminal-justice system, the report said.

Already, the report's numbers are being treated with some caution by some criminal-justice experts, who say that the report could even be an underestimation of the full impact on women in jails.

John Pfaff, a professor at Fordham Law School, noted on Twitter that while the country's jail population may be 745,000, that number is totaled just once a year, and so doesn't show the 11 million jail admissions that occur throughout the course of each year.

Pfaff also noted that while the rate of women's incarcerations between 1970 and 2014 may have quadrupled, men still account for nearly 83% of the overall increase in jail populations.